7 Causes of Electrical Discharge Machining in Bearings

Electrical discharge machining (EDM) occurs when electrical current passes through a bearing instead of following its intended grounding path. As the current discharges, it creates microscopic arcs that pit bearing surfaces and raceways. Over time, those pits turn into fluting, vibration, noise, and early bearing failure.

While the damage shows up mechanically, the root causes are almost always electrical. Here are the most common reasons EDM develops in industrial bearings:

Table of Contents

1. Variable frequency drives

Variable frequency drives (VFDs) are the leading cause of EDM-related bearing damage. High-frequency switching creates common-mode voltage that seeks a path to ground. When proper grounding or shaft grounding is missing, the bearing becomes the discharge route. Repeated discharges pit the raceways until fluting forms and failure accelerates.

2. Poor or inadequate grounding

When motors, drives, or equipment frames aren’t properly grounded, electrical energy looks for alternative paths. Bearings often become that unintended route. Loose ground connections, high-impedance grounding, or incomplete bonding increase the likelihood of current passing through bearing assemblies.

3. Shaft voltage buildup

Shaft voltage builds when electrical energy accumulates on the motor shaft faster than it can dissipate. This is common in systems with high switching frequencies or long cable runs. Once the voltage exceeds the lubricant’s dielectric strength, it discharges through the bearing, creating an EDM event.

4. Improper cable shielding or termination

Poorly shielded motor cables or incorrect shield termination allow electrical noise to propagate through the system. This increases common-mode voltage and stray currents. Without a controlled path to ground, that energy often discharges through bearings instead of safely returning through the electrical system.

5. Insulated couplings or driven equipment

When motors are connected to gearboxes, pumps, or loads with insulated couplings, normal grounding paths can be interrupted. This forces shaft currents to find another way out. Bearings frequently become the easiest route, especially in systems with VFDs or high-frequency electrical noise.

6. Inadequate bearing lubrication

Lubrication acts as an electrical insulator — up to a point. When lubricant films break down due to contamination, overheating, or improper viscosity, their dielectric strength drops. This allows electrical discharge to pass through the bearing more easily, increasing EDM frequency and severity.

7. Long motor lead lengths

Extended cable lengths between the drive and motor amplify reflected wave voltage and common-mode effects. These conditions increase shaft voltage and stray currents. Without mitigation — such as proper grounding, filters, or shaft grounding devices — bearings absorb the electrical stress.

Electrical discharge machining doesn’t start in the bearing but rather in the electrical system feeding it. Once bearings become part of the electrical circuit, damage is only a matter of time. By addressing grounding, drive configuration, cabling, lubrication, and shaft voltage control, teams can eliminate EDM at the source and extend bearing life.

Ultimately, treating EDM as an electrical reliability issue — not just a bearing failure — changes the outcome.

If bearing failures are happening faster than expected or showing signs of fluting or pitting, Global Electronic Services can help identify the electrical causes behind the damage. Contact us for Repair, Sales & Service of Industrial Electronics, Servo Motors, AC & DC Motors, Hydraulics & Pneumatics — don’t forget to like and follow us on Facebook, LinkedIn, YouTube, and X!